Method for producing lacquered thin sheets of aluminum



It is well known to use sheets of aluminum or aluminum alloy inlacquered or unlacquered state as a substitute material for tin plate.ample of the fabrication of cans or boxes or bottle caps of the crowncork type, sheets of a thickness of at most 0.8 mm. and at least 0.1mm., preferably between 0.25' and 0.35 mm, are required. The aluminumsheets which have been furnished till now for such purposes and whichare produced in the form of a rolled strip have a mechanical strengthbelow that of the tin plate, especially if they were used lacquered- Ifa hard rolled sheet of aluminum or an aluminum alloy with only a littleamount of alloying constituents is used lacquered, whereby the varnishserves as protection against corrosion or as a priming coat for aplastic coating, the metal looses its mechanical strength during heatingfor drying or baking the varnish, so that its strength is not sufiicientfor cans and crown corks. Sheets of highly alloyed aluminum, for examplewith magnesium, which have also in the annealed state considerabletensile strength, yield strength, elongation and hardness, are notsuitable as a substitute material for tin plate in the making of massproduced articles such as cans and crown corks because of their higherprice. The material of the sheet should not cost sensibly more than purealuminum.

Our present invention relates to a method for producing lacquered thinsheets of aluminum, the mechanical properties of which correspond tothose of tin plate of the same thickness and which may also compete inprice with tin plate.

According to our invention an aluminum alloy containing at most 1.5% ofone or more of the alloying constituents Mg, Si, Zn, Cr, Mn and Ti issolution annealed and quenched at least at the double end thickness,preferably at the 3- to 5-fold and thickness, is aged at roomtemperatureor slightly increased temperature, for example at 40 to 60 C., in orderto attain a natural aging effect, then rolled to end thickness,thereafter coated with the solution of a varnish giving a coatingsuitable for deep-drawing and finally heated for drying or baking thevarnish, whereby in comparison to the cold rolled state not only themalleability but also the mechanical strength of the sheet is increased.

It the solution annealing is carried out at the double end thickness,the sheet becomes then cold rolled with a deformation degree of 50%; ifthe solution treatment is carried out at the fivefold end thickness, thecold rolling degree will be 80%. This value may be exceeded if thedesired mechanical strength is still reached. 1

The aging for attaining a natural aging effect is preferably carried outuntil practically the state of full agehardening is reached. For examplewith an alurninum alloy with 0.4% Mg and 0.6% Si it is recommendable tochoose an aging period of at least two days at room temperature,respectively somewhat shorter at a slightly increased temperature.

Preferably this alloy is aged at room temperature during 3 to 4 days. Ofcourse a longer aging period is not detrimental as the material remainsunchanged after aging. 7

There may be considered many aluminum alloys with If it is the questionfor eX- of crown corks.

strength and the hardness.

3,032,448 Patented May 1, 1962 a low content of alloying constituents,but for the practice of the present invention they must be harde-nableby a heat treatment. Very good results are obtained with sheets of analuminum alloy containing about 0.3- to 0.7% Mg and 0.3 to 0.7% Si. Thealuminum with a low content of alloying constituents may of coursecontain beside Mg, Si, Zn, Cr, Mn and Ti some; other elements in a lowamount, provided that these other elements do not impair the result ofthe method according to the invention.

The sheet of aluminum alloy is preferably rolled and worked subsequentlyas a strip. After drying or stoving the varnish the sheet is cut,punched, divided in several increase results during cold rolling, butsimultaneously the elongation is decreased. With an aluminum alloycontaining 0.4% Mg and 0.6% Si the elongation drops to 6 t0 3%. In thisstate the malleability is not sufiicient for example for the deepdrawing of cans or for the making But when the cold rolled sheet hasbeen lacquered and is heated during 10 minutes, to 30 seconds at atemperature of 120 to 240 C. for drying or stoving the varnish it issubjected at the same time to a re laxation of the crystalline structureresulting in an increase of the elongation for example up to 10-15% anda subsequent increase of the tensile strength, the yield The improvementof the mechanical properties of the cold rolled sheet is combined withthe drying or stoving of the lacquer coating.

It was already known to lacquer after solution annealing and quenchingarticles made of an aluminum alloy containing 0.6 to 1.4% Mg, 0.8 to1.2% Si, 0.6 to 1.0% Mn and up to 0.3% Cr (known in Europe as AlMgSi)and to heat them thereafter in order to stove the varnish and to age thealloy at the same time. But it was the question neither of an aluminumalloy with a low content of alloying constituents nor of the lacqueringand arof the several working steps: solution annealing, quenching,natural aging, cold rolling, artificial aging together withdrying andstoving the lacquer, it was possible to increase the tensile strength,the yield strength, the hardness and the elongation and also to dry thevarnish. Without the natural aging after the solution annealing andquenching it is not possible to obtain a sufficient mechanical strengthby artificially aging a sheet of an end thickness of for example 0.25 to0.45 mm. if the sheet should be used for the fabrication of cans orcrown corks.

The methodaccording to our invention presents besides the alreadymentioned advantages (steady improvement of the mechanical strengthduring the last working steps, combination of the artificial aging withthe drying and stoving of the varnish) further advantages:

(1) The solution annealing and the quenching have not to be carried outat the end thickness of the sheet, but can be done at a considerablehigher thickness. A hardening by solution annealing and quenching at anend thickness of for example 0.25 to 0.45 mm. is uneconomical,technically difiicult to be carried out and does not give the maximalvalues for the mechanical strength.

(2) Generally the surface of the hardenable aluminum alloys, even of thealloys with a low content of alloying constituents, shows a grey colourafter solution annealing and quenching, which colour does not disappearduring aging. But during the cold rolling of the aged material accordingto our invention the surface becomes bright again, what is veryadvantageous for the use of the material.

Example.--A strip of aluminum containing 0.4% Mg and 0.6% Si is solutionannealed at an intermediate thickness of 1 to 1.5 mm. quenched in coldwater and naturally aged, whereby the yield strength is increased from4-6 kg./mm. up to 8-15 kg./mm. the tensile strength from about 10 up toabout kgjmm. and the Brinell hardness from 20-30 up to -60 kg/rnmfi.During the following cold rolling to the end thickness of 0.3 mm.(deformation degree of to the yield strength rises to 2834 kg./mm. thetensile strength to 30-35 kg./mm. and the Brinell'hardness to -100kg./rnm. In this state the elongation is only 3 to 4%, that means themalleability is insutiicient for example for the manufacture of crowncorks. It now such a cold rolled sheet is then lacquered according toany known method and the varnish is dried by heating at a temperaturebetween and 240 C., the elongation becomes considerably increased; itsvalue may rise up to 15%, whereas yield strength and tensile strength donot decrease, but increase further by about 6 to 8% respectively 8 to10%. The mechanical strength of the material obtained in this waycorresponds to the strength of the usual tin plate of the samethickness.

What we claim is:

1. The method for producing lacquered thin, deformable sheets ofaluminum with high mechanical strength comprising the steps of solutionannealing and quenching to room temperature a rolled sheet of analuminum alloy containing at least one of the constituents selected froma group consisting of Mg, Si, Zn, Cr, Mn and Ti, in an amount not toexceed 1.5% by weight, the said constituents being in such combinationand amount that the alloy is hardenable by heat treatment, theseannealing and quenching steps taking place at a thickness at least twicethe desired ultimate thickness of the sheet; aging the sheet forattaining a natural aging effect; cold rolling the sheet to endthickness; covering the sheet with the solution of a varnish giving acoating suitable for deepdrawing and heating the lacquered sheet to 120to 240 C. for drying or stoving the varnish, whereby not only themalleability but also the mechanical strength of the sheet becomeincreased in comparison to the mechanical strength of the sheet in thecold-rolled state.

2. The method according to claim 1, in which the sheet is worked instrip form.

3. The method according to claim 1, in which the sheet is made from analloy consisting of aluminum, 0.3 to 0.7% Mg and 0.3 to 0.7% Si.

4. The method according to claim 1, in which the sheet is cold rolled toa thickness of 0.8 to 0.1 mm.

References Cited in the file of this patent UNITED STATES PATENTS1,083,903 Wilm Jan. 6, 1914 1,472,739 Archer et a1 Oct. 30, 19232,394,546 Harrington Feb. 12, 1946 2,695,253 Schaaber Nov. 23, 19542,837,450 Moore et a1. June 3, 1958 2,877,195 McNa-bb Mar. 10, 1959

1. THE METHOD FOR PRODUCING LACQUERED THIN, DEFORMABLE SHEETS OFALUMINUM WITH HIGH MECHANICAL STRENGTH COMPRISING THE STEPS OF SOLUTIONANNEALING AND QUENCHING TO ROOM TEMPERATURE A ROLLED SHEET OF ANALUMINUM ALLOY CONTAINING AT LEAST ONE OF THE CONSTITUENTS SELECTED FROMA GROUP CONSISTING OF MG, SI, ZN, CR, MN AND TI, IN AN AMOUNT NOT TOEXCEED 1.5% BY WEIGHT, THE SAID CONSTITUENTS BEING IN SUCH COMBINATIONAND AMOUNT THAT THE ALLOY IS HARDENABLE BY HEAT TREATMENT, THESEANNEALING AND QUENCHING STEPS TAKING PLACE AT A THICKNESS AT LEAST TWICETHE DESIRED ULTIMATE THICKNESS OF THE SHEET; AGING THE SHET FORATTAINING A NUTRAL AGING EFFECT; COLD ROLLING THE SHEET TO ENDTHICKNESS; COVERING THE SHEET WITH THE SOLUTION OF A VARNISH GIVING ACOATING SUITABLE FOR DEEPDRAWING AND HEATING THE LACQUERED SHEET TO 120TO 240* C. FOR DRYING OR STOVING THE VARNISH, WHEREBY NOT ONLY THEMALLEABILITY BUT ALSO THE MECHANICAL STRENGTH OF THE SHEET BECOMEINCREASED IN COMPARISON TO THE MECHANICAL STRENGTH OF THE SHEET IN THECOLD-ROLLED STATE.